utor

Utor, uti, usus sum is deponent and third conjugation, and the one thing that matters about it is the case it takes: the ablative, never the accusative. Gladio utitur, not gladium utitur. It shares that ablative with fruor, fungor, potior and vescor, and grammars teach the five as a set for exactly that reason.

Because it is deponent, usus sum means "I used", not "I was used", and the participle usus is active in sense: usus gladio is "having used a sword". The perfect is periphrastic, so the corpus form usi will normally have a form of sum somewhere nearby. Off the same stem come the noun usus, "use, experience", the adjective utilis, "useful", and English use, utility, utensil, usury and abuse.